A wavelength selective switch (WSS) is used to dynamically attenuate, block, switch and route wavelengths independently. Since WSS are used in management of live optical networks, they have to be highly reliable, which includes great tolerance to mechanical shock and environmental conditions.
A WWS is an N-port module composed of a hermetically sealed block of optics and control electronics; optical fibers are soldered thereto. Hermetic sealing of optical fibers to a package is a key aspect of hermetic packaging technology for WSS modules. However, tensile stresses in the soldered joints often cause cracking of the solder, which compromise the seal and negatively affect compliance with the industry requirements.
Typically, an optical fiber is soldered into a fiber ferrule which has a high coefficient of thermal expansion (CTE) so as to provide a compressive solder-to-fiber seal. The main requirement for a package material is to have a low CTE because of (a) optomechanical stability considerations as optical components may be rigidly attached to the package; (b) thermally match any low CTE ceramic/glass material that may be part of the package. The conflicting CTE requirements for a package and a fiber ferrule pose a challenge to reliability of the package to fiber-ferrule seal; namely presence of large tensile stresses in the seal causing premature fatigue failure of the solder joint under thermal cycling.
An object of the present invention is to eliminate, or at least minimize, negative effects of tensile stress between an optical fiber ferrule and a package and to provide a hermetic feedthrough of an optical fiber and a package, and a method of forming thereof.